os: add norm_path and abs_path function (#14435)

vlib/os/filepath.v

@@ -1,13 +1,20 @@
 module os
 
+import strings
+import strings.textscanner
+
 // Collection of useful functions for manipulation, validation and analysis of system paths.
 // The following functions handle paths depending on the operating system,
 // therefore results may be different for certain operating systems.
 
 const (
-	fslash = `/`
-	bslash = `\\`
-	dot    = `.`
+	fslash  = `/`
+	bslash  = `\\`
+	dot     = `.`
+	qmark   = `?`
+	dot_dot = '..'
+	empty   = ''
+	dot_str = '.'
 )
 
 // is_abs_path returns `true` if the given `path` is absolute.
@@ -16,11 +23,152 @@ pub fn is_abs_path(path string) bool {
 		return false
 	}
 	$if windows {
-		return is_device_path(path) || is_drive_rooted(path) || is_normal_path(path)
+		return is_unc_path(path) || is_drive_rooted(path) || is_normal_path(path)
 	}
 	return path[0] == os.fslash
 }
 
+// abs_path joins the current working directory
+// with the given `path` (if the `path` is relative)
+// and returns the absolute path representation.
+pub fn abs_path(path string) string {
+	wd := getwd()
+	if path.len == 0 {
+		return wd
+	}
+	npath := norm_path(path)
+	if npath == os.dot_str {
+		return wd
+	}
+	if !is_abs_path(npath) {
+		mut sb := strings.new_builder(npath.len)
+		sb.write_string(wd)
+		sb.write_string(path_separator)
+		sb.write_string(npath)
+		return norm_path(sb.str())
+	}
+	return npath
+}
+
+// norm_path returns the normalized version of the given `path`
+// by resolving backlinks (..), turning forward slashes into
+// back slashes on a Windows system and eliminating:
+// - references to current directories (.)
+// - redundant path separators
+// - the last path separator
+[direct_array_access]
+pub fn norm_path(path string) string {
+	if path.len == 0 {
+		return '.'
+	}
+	rooted := is_abs_path(path)
+	volume := get_volume(path)
+	volume_len := volume.len
+	cpath := clean_path(path[volume_len..])
+	if cpath.len == 0 && volume_len == 0 {
+		return '.'
+	}
+	spath := cpath.split(path_separator)
+	if os.dot_dot !in spath {
+		return if volume_len != 0 { volume + cpath } else { cpath }
+	}
+	// resolve backlinks (..)
+	spath_len := spath.len
+	mut sb := strings.new_builder(cpath.len)
+	if rooted {
+		sb.write_string(path_separator)
+	}
+	mut new_path := []string{cap: spath_len}
+	mut backlink_count := 0
+	for i := spath_len - 1; i >= 0; i-- {
+		part := spath[i]
+		if part == os.empty {
+			continue
+		}
+		if part == os.dot_dot {
+			backlink_count++
+			continue
+		}
+		if backlink_count != 0 {
+			backlink_count--
+			continue
+		}
+		new_path.prepend(part)
+	}
+	// append backlink(s) to the path if backtracking
+	// is not possible and the given path is not rooted
+	if backlink_count != 0 && !rooted {
+		for i in 0 .. backlink_count {
+			sb.write_string(os.dot_dot)
+			if new_path.len == 0 && i == backlink_count - 1 {
+				break
+			}
+			sb.write_string(path_separator)
+		}
+	}
+	sb.write_string(new_path.join(path_separator))
+	res := sb.str()
+	if res.len == 0 {
+		if volume_len != 0 {
+			return volume
+		}
+		if !rooted {
+			return '.'
+		}
+		return path_separator
+	}
+	if volume_len != 0 {
+		return volume + res
+	}
+	return res
+}
+
+// clean_path returns the "cleaned" version of the given `path`
+// by turning forward slashes into back slashes
+// on a Windows system and eliminating:
+// - references to current directories (.)
+// - redundant separators
+// - the last path separator
+fn clean_path(path string) string {
+	if path.len == 0 {
+		return ''
+	}
+	mut sb := strings.new_builder(path.len)
+	mut sc := textscanner.new(path)
+	for sc.next() != -1 {
+		curr := u8(sc.current())
+		back := sc.peek_back()
+		peek := sc.peek()
+		// skip current path separator if last byte was a path separator
+		if back != -1 && is_slash(u8(back)) && is_slash(curr) {
+			continue
+		}
+		// skip reference to current dir (.)
+		if (back == -1 || is_slash(u8(back))) && curr == os.dot
+			&& (peek == -1 || is_slash(u8(peek))) {
+			// skip if the next byte is a path separator
+			if peek != -1 && is_slash(u8(peek)) {
+				sc.skip_n(1)
+			}
+			continue
+		}
+		// turn foward slash into a back slash on a Windows system
+		$if windows {
+			if curr == os.fslash {
+				sb.write_u8(os.bslash)
+				continue
+			}
+		}
+		sb.write_u8(u8(sc.current()))
+	}
+	res := sb.str()
+	// eliminate the last path separator
+	if res.len > 1 && is_slash(res[res.len - 1]) {
+		return res[..res.len - 1]
+	}
+	return res
+}
+
 // win_volume_len returns the length of the
 // Windows volume/drive from the given `path`.
 fn win_volume_len(path string) int {
@@ -32,7 +180,7 @@ fn win_volume_len(path string) int {
 		return 2
 	}
 	// its UNC path / DOS device path?
-	if path.len >= 5 && starts_w_slash_slash(path) && !is_slash(path[2]) {
+	if plen >= 5 && starts_w_slash_slash(path) && !is_slash(path[2]) {
 		for i := 3; i < plen; i++ {
 			if is_slash(path[i]) {
 				if i + 1 >= plen || is_slash(path[i + 1]) {
@@ -51,6 +199,20 @@ fn win_volume_len(path string) int {
 	return 0
 }
 
+fn get_volume(path string) string {
+	$if !windows {
+		return ''
+	}
+	volume := path[..win_volume_len(path)]
+	if volume.len == 0 {
+		return ''
+	}
+	if volume[0] == os.fslash {
+		return volume.replace('/', '\\')
+	}
+	return volume
+}
+
 fn is_slash(b u8) bool {
 	$if windows {
 		return b == os.bslash || b == os.fslash
@@ -58,7 +220,7 @@ fn is_slash(b u8) bool {
 	return b == os.fslash
 }
 
-fn is_device_path(path string) bool {
+fn is_unc_path(path string) bool {
 	return win_volume_len(path) >= 5 && starts_w_slash_slash(path)
 }